Low power system and method for DSL lines

ABSTRACT

The transmit power level of a transceiver coupled to a digital subscriber line (DSL) line is reduced from a first transmit power level sufficient for the transceiver to continuously transmit data on the DSL line at a first bit rate to a second transmit power level below the first transmit power level sufficient for the transceiver to continuously transmit data on the DSL line at a second bit rate that is lower than the first bit rate. The reduction in transmit power is limited so that the change does not induce time-varying crosstalk sufficient to destabilize a nearby DSL line. While the transmit power level of the transceiver is reduced to the second transmit power level, the transceiver is suspended from transmitting data on the DSL line for repeated periods of time. Suspending the data transmission is controlled to avoid further time-varying crosstalk sufficient to destabilize the nearby DSL line.

CLAIM FOR PRIORITY

This application is a 371 National Phase application of, and claimspriority to PCT Patent Application Serial No. PCT/US2013/057672, filedon 30 Aug. 2013, titled “LOW POWER SYSTEM AND METHOD FOR DSL LINES,” andwhich is incorporated by reference in entirety.

COPYRIGHT NOTICE

A portion of the disclosure of this patent document contains materialthat is subject to copyright protection. The copyright owner has noobjection to the facsimile reproduction by anyone of the patent documentor the patent disclosure, as it appears in the Patent and TrademarkOffice patent file or records, but otherwise reserves all copyrightrights whatsoever.

TECHNICAL FIELD

The subject matter described herein relates generally to the field ofcommunication systems and more specifically to a method and apparatusfor reducing power consumption and noise in a communication system.

BACKGROUND

Digital Subscriber Line (DSL) lines are often underutilized, at timestransmitting little or no data, which is an inefficient use of power. Itmay take a minute or more to re-start a DSL line that has beencompletely turned off. Thus, completely turning off a DSL line to savepower often causes undesirable delay in re-starting the DSL line. Thereare many times when it would be desirable to transmit data on the DSLline at low bit-rates sufficient, for example, to transmit keep-alivesand/or possibly certain types of data traffic, such as low levels ofInternet data traffic, or Voice over Internet Protocol (VoIP) datatraffic, with very low power consumption.

The low-power states used in current DSL line transmission standardssuch as ADSL2 and ADSL2plus [ITU-T standards G.992.3 and G.992.5] cansave power on DSL lines by lowering the transmit power and the transmitpower spectral density (PSD), and using lower bit loading to carrytraffic on the DSL line at a lower bit rate. This low-power state isreferred to “L2-mode.” L2-mode can lower transmit power by up to 31 dBtotal maximum aggregate transmit power reduction in L2-mode (L2-ATPRT).

FIG. 2 illustrates a typical DSL environment 200 in which two DSL linesare located within the same cable. In particular, the telephone localloop or cable 112 is coupled from Digital Subscriber Line AccessMultiplexer (DSLAM)/AN 114 to one or more TU-R units, for example, TU-R122 a and TU-R 122 b. Multiple DSL lines may exist within the cable, forexample, DSL line 112 a coupled from TU-C 142 a to TU-R 122 a, andnearby DSL line 112 b coupled from TU-C 142 b to TU-R 122 b. DSL linesadapt to the channel and noise levels at start-up, and if the noisesubsequently increases by a level at or above the signal to noise ratio(SNR) margin then the DSL line can become unstable and resynchronize.Much of the noise is “crosstalk”, such as depicted at 205, from otherDSL lines using the same cable, in the same loop, or in the same binder,caused by transmitting signals in both the downstream direction 210and/or the upstream direction 215. A potential problem with low powerstates on a DSL line is that they can create time-varying crosstalk,also referred to as fluctuating crosstalk, non-stationary crosstalk, orshort-term stationary crosstalk in nearby or neighboring DSL lines.Raising and lowering the transmit power or transmit PSD levels ofsignals transmitted on the DSL line also raises and lowers the crosstalkreceived by nearby DSL lines. If the crosstalk abruptly or suddenlyincreases by a large amount then one or more of these nearby DSL linesmay need to resynchronize; such “instability” is highly undesirable.Resynchronization can be avoided by certain methods including slowlyexiting from the low-power states, as described in U.S. patentapplication Ser. No. 12/700,892 entitled Apparatus, Systems and Methodsfor DSM Energy Management, assigned to the assignee of this patentapplication. Such methods allow nearby DSL lines sufficient time toadapt to the higher crosstalk level induced by increasing the transmitpower and transmit PSD levels of signals transmitted on a DSL line viaseamless rate adaptation (SRA) or other techniques. However, the currentDSL standards and DSL equipment do not allow slow exit from low-powermode; it can only be done rapidly, as set forth in ITU-T G.992.3 andG.992.5, and Broadband Forum TR-202, which creates instability in nearbyDSL lines. Further, while low-power states may be gradually entered,this does little to help stability. Power consumption can also bereduced by suspending data transmission on a DSL line entirely for briefmoments when there is no data traffic to transmit, or by queuing thedata traffic for transmission at a later time. This suspension of datatraffic on the DSL line is referred to as “discontinuous operation.”With reference to FIG. 3, discontinuous operation 300 involves the DSLtransceiver's transmitter turning “ON” and transmitting at some times(305, 315, 325 and 335), and turning “OFF” the transmitter at othertimes (310, 320, and 330). The duration of the ON and OFF times could beany possible value. Alternatively, to ensure synchronization of the DSLline or to track channel variations on the DSL line the maximum OFF timeand/or the minimum ON time may be specified. FIG. 3 illustrates at 340,345 and 350 turning on the transmitter, for example, when trafficarrives at the transmitter, when the amount of traffic arriving at thetransmitter increases, when a queue maintained by the transceiver inwhich traffic to be transmitted by the transmitter reaches a certainthreshold, or when a timer reaches a certain time or time out value.When there is no traffic to transmit, the transmitter may be turned OFF.Turning the transmitter OFF may even involve briefly turning off DSLtransceiver functionality entirely, which could enable large powersavings. Discontinuous operation is generally performed in real-time, insub-second on/off duration times. Discontinuous operation can, however,cause very large and frequent fluctuations in crosstalk and can causewidespread instability problems in neighboring DSL lines. Also, a DSLline that doesn't transmit for a long time may itself losesynchronization and not properly track the channel.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments are illustrated by way of example, and not by way oflimitation, and can be more fully understood with reference to thefollowing detailed description when considered in connection with thefigures in which:

FIG. 1 illustrates an exemplary architecture in which embodiments of theinvention may operate.

FIG. 2 illustrates crosstalk between two DSL lines in the same cable.

FIG. 3 illustrates discontinuous operation of a DSL line in exemplaryembodiments of the invention.

FIG. 4 illustrates an example of different power states (circles), andallowed transitions between power states (lines with arrowheads showingthe direction of the allowed state transitions), according toembodiments of the invention.

FIG. 5 illustrates low-power state transitions according to embodimentsof the invention.

FIG. 6 illustrates DSL line and low-power state transitions according toembodiments of the invention.

FIG. 7 illustrates examples of different transmitted low-power mode(LPM) power spectral densities (PSDs) according to embodiments of theinvention.

DETAILED DESCRIPTION

Embodiments of the invention relate to a system and method of low-poweroperation for DSL lines that combines the use of lower transmit power orlower transmit power spectral density (PSD) with the use ofdiscontinuous operation. In one embodiment of the invention, there arefour exemplary power states: full power (L0), low transmit power ortransmit PSD level (L2.0), lowest transmit power or transmit PSD level(L2.1), and a low transmit power or transmit PSD level combined withdiscontinuous operation (L2.2). Discontinuous operation is not usedexcept when the transmit power or transmit PSD is at a low enough levelthat the crosstalk induced by such into neighboring DSL lines does notdestabilize the lines. Such embodiments enable a very low power usage,since both the transmit PSD is lowered and DSL transceiver functionalitycan be intermittently turned off with discontinuous operation. Asdescribed further below, some embodiments further incorporate amanagement system that optimizes DSL settings for a given DSL line toenhance performance, increase power savings, and maintain stability ofnearby DSL lines. Embodiments of the invention create a particularlyuseful set of low-power transmission states and manage the transitionsbetween these states, with DSL data throughput, power usage, andcrosstalk impacts all varying synergistically between the states.

Embodiments of the invention are primarily targeted for use with VDSL2or G.fast, but may be applied to any DSL technology. As used herein, theterm “DSL” refers to any of a variety and/or variant of DSL technologysuch as, for example, Asymmetric DSL (ADSL), ADSL2, ADSL2plus,High-speed DSL (HDSL), HDSL2, Symmetric DSL (SDSL), SHDSL, Veryhigh-speed/Very high-bit-rate DSL (VDSL), VDSL2, vectored VDSL2, and/orG.fast. Such DSL technologies are commonly implemented in accordancewith an applicable standard such as, for example, the InternationalTelecommunications Union (I.T.U.) standard G.992.1 (a.k.a. G.dmt) forADSL modems, the I.T.U. standard G.992.3 (a.k.a. G.dmt.bis, or G.adsl2)for ADSL2 modems, I.T.U. standard G.992.5 (a.k.a. G.adsl2plus) forADSL2+ modems, I.T.U. standard G.993.1 (a.k.a. G.vdsl) for VDSL modems,I.T.U. standard G.993.2 for VDSL2 modems, I.T.U. standard G.993.5 forDSL modems supporting Vectoring, I.T.U. standard G.998.4 for DSL modemssupporting retransmission, I.T.U. standard G.994.1 (G.hs) for modemsimplementing handshake, and/or the I.T.U. G.997.1 (a.k.a. G.ploam)standard for management of DSL modems. The G.997.1 standard specifiesthe physical layer management for ADSL transmission systems based on theclear, Embedded Operation Channel (EOC) defined in G.997.1 and use ofindicator bits and EOC messages defined in the G.992.x, G.993.x andG.998.4 standards. Moreover, G.997.1 specifies network managementelements content for configuration, fault and performance management. Inperforming the disclosed functions, systems may utilize a variety ofoperational data (which includes performance data) that is available atan Access Node (AN). The DSL lines with low-power states and the DSLlines receiving crosstalk, as described herein, may be any of these DSLtypes.

FIG. 1 illustrates an exemplary architecture 100 in which embodimentsmay operate in compliance with the foregoing standards. In FIG. 1,user's terminal equipment 102 (e.g., a Customer Premises Equipment (CPE)device or a computer, network node, LAN device, etc.) is coupled to ahome network 104, which in turn is coupled to a Network Termination (NT)Unit 108. Multiple xTU devices (“all Transceiver Unit” devices) arefurther depicted. An xTU provides modulation for a DSL loop or line(e.g., DSL, ADSL, VDSL, etc.). In one embodiment, NT unit 108 includesan xTU-R (xTU Remote), 122 (for example, a transceiver defined by one ofthe ADSL or VDSL standards) or any other suitable network terminationmodem, transceiver or other communication unit. NT unit 108 alsoincludes a Management Entity (ME) 124.

Management Entity 124 may be any suitable hardware device, such as amicroprocessor, microcontroller, or circuit state machine in firmware orhardware, capable of performing as required by any applicable standardsand/or other criteria. Management Entity 124 collects and stores, amongother things, operational data in its Management Information Base (MIB),which is a database of information maintained by each ME capable ofbeing accessed via network management protocols such as Simple NetworkManagement Protocol (SNMP), an administration protocol used to gatherinformation from a network device to provide to an administratorconsole/program; via Transaction Language 1 (TL1) commands, TL1 being along-established command language used to program responses and commandsbetween telecommunication network elements; via embedded operationschannel (eoc) signaling over the DSL line, or via a TR-69 basedprotocol. “TR-69” or “Technical Report 069” is in reference to a DSLForum technical specification entitled CPE WAN Management Protocol(CWMP) that defines an application layer protocol for remote managementof end-user devices. XML or “eXtended Markup Language” compliantprogramming and interface tools may also be used.

In one embodiment, Network Termination Unit 108 is communicablyinterfaced with a management device 170 as described herein. In anotherembodiment, xTU-R 122 is communicably interfaced with management device170. Each xTU-R 122 in a system may be coupled with an xTU-C (xTUCentral) in a Central Office (CO) or other central location. The xTU-C142 is located at an Access Node (AN) 114 in Central Office 146. AManagement Entity (ME) 144 likewise maintains an MIB of operational datapertaining to xTU-C 142. The Access Node 114 may be coupled to abroadband network 106 or other network, as will be appreciated by thoseskilled in the art. Each of xTU-R 122 and xTU-C 142 are coupled togetherby a U-interface/loop 112, which in the case of ADSL may be a twistedpair line, such as a telephone line, which may carry other communicationservices besides DSL based communications. Either Management Entity 124or Management Entity 144 may implement and incorporate a managementdevice 170 as described herein.

Management device 170 may be managed or operated by a service providerof the DSL services or may be operated by a third party, separate fromthe entity which provides DSL services to end-users. Thus, in accordancewith one embodiment apparatus 170 is operated and managed by an entitythat is separate and distinct from a telecommunications operatorresponsible for a plurality of digital communication lines. ManagementEntity 124 or Management Entity 144 may further store informationcollected from apparatus 170 within an associated MIB.

Several of the interfaces shown in FIG. 1 are used for determining andcollecting operational data. The Q interface 126 provides the interfacebetween the Network Management System (NMS) 116 of the operator and ME144 in Access Node 114. Parameters specified in the G.997.1 standardapply at the Q interface 126. The near-end parameters supported inManagement Entity 144 may be derived from xTU-C 142, while far-endparameters from xTU-R 122 may be derived by either of two interfacesover the U-interface. Indicator bits and EOC messages may be sent usingembedded channel 132 and provided at the Physical Medium Dependent (PMD)layer, and may be used to generate the required xTU-R 122 parameters inME 144. Alternately, the Operations, Administration and Maintenance(OAM) channel and a suitable protocol may be used to retrieve theparameters from xTU-R 122 when requested by Management Entity 144.Similarly, the far-end parameters from xTU-C 142 may be derived byeither of two interfaces over the U-interface. Indicator bits and EOCmessage provided at the PMD layer may be used to generate the requiredxTU-C 142 parameters in Management Entity 124 of NT unit 108.Alternately, the OAM channel and a suitable protocol may be used toretrieve the parameters from xTU-C 142 when requested by ManagementEntity 124. Additionally depicted is G-interface 160 between NMS 116 andbroadband network 160.

At the U-interface (also referred to as local loop, or simply loop 112),there are two management interfaces, one at xTU-C 142 (the U-C interface158) and one at xTU-R 122 (the U-R interface 157). The U-C interface 158provides xTU-C near-end parameters for xTU-R 122 to retrieve over theU-interface/loop 112. Similarly, the U-R interface 157 provides xTU-Rnear-end parameters for xTU-C 142 to retrieve over the U-interface/loop112. The parameters that apply may be dependent upon the transceiverstandard being used (for example, G.992.5 or G.993.2). The G.997.1standard specifies an optional Operation, Administration, andMaintenance (OAM) communication channel across the U-interface. If thischannel is implemented, xTU-C and xTU-R pairs may use it fortransporting physical layer OAM messages. Thus, the xTU transceivers 122and 142 of such a system share various operational data maintained intheir respective MIBs.

Depicted within FIG. 1 is management device 170 operating at variousoptional locations in accordance with several alternative embodiments.For example, management device 170 is located within home network 104,such as within a LAN. In an alternative embodiment, management device170 is located at central office 146 and interfaced to home network 104(e.g., a LAN) and broadband network 106 (e.g., DSL) via NMS 116. In yetanother embodiment, management device 170 operates on the broadbandnetwork 106 (e.g., on the DSL). In one embodiment apparatus 170 operatesas a DSL modem, such as a Customer Premises (CPE) modem. In anotherembodiment, apparatus 170 operates as a controller card or as a chipsetwithin a user's terminal equipment 102 (e.g., a Customer PremisesEquipment (CPE) device or a remote terminal device, network node, LANdevice, etc.) coupled to the home network 104 as depicted. In anotherembodiment, apparatus 170 operates as a separate and physically distinctstand-alone unit which is connected between the user's terminalequipment 102 and a DSL line or loop. For example, apparatus 170 mayoperate as a stand-alone signal-conditioning device. In yet anotherembodiment, apparatus 170 is connected with a NT unit 108 or with xTU-R122 over the T/S interface 159.

As used herein, the terms “user,” “subscriber,” and/or “customer” referto a person, business and/or organization to which communicationservices and/or equipment are and/or may potentially be provided by anyof a variety of service provider(s). Further, the term “customerpremises” refers to the location to which communication services arebeing provided by a service provider. For an example Public SwitchedTelephone Network (PSTN) used to provide DSL services, customer premisesare located at, near and/or are associated with the network termination(NT) side of the telephone lines. Example customer premises include aresidence or an office building. As used herein, the term “serviceprovider” refers to any of a variety of entities that provide, sell,provision, troubleshoot and/or maintain communication services and/orcommunication equipment. Example service providers include a telephoneoperating company, a cable operating company, a wireless operatingcompany, an Internet service provider, or any service that mayindependently or in conjunction with a broadband communications serviceprovider offer services that diagnose or improve broadbandcommunications services (DSL, DSL services, cable, etc.).

Power States

Table 1 below defines the DSL low-power states considered in oneembodiment of the invention. State L2.0 may in one embodiment contain anarray of substates, where each substate L2.0-x is identified by thenumber, x, indicating the transmit power reduction below full power, asmeasured in dB.

TABLE 1 DSL Power States Transmit power & Informal name State transmitPSD level Operation Full-power L0 (aka L0.0) Full power ContinuousReduced power L0 L2.0 Reduced power and Continuous (reduced by x dB)Substates: L2.0-x transmit PSD VoIP and keep alive L2.1 Maximallyreduced Continuous (at least 256 kbps) power and transmit PSD Keep aliveL2.2 Maximal (or near Dis- maximal) reduced continuous power andtransmit PSD

Continuous operation refers to constantly transmitting signals acrossthe DSL line, and if there is no data to transmit then dummy or pad bitsare transmitted. DSL lines normally transmit continuously. Discontinuousoperation suspends transmission when there is no data traffic to send,or when data traffic transmission can be suspended, the data trafficqueued during suspension, and then later resumed. Discontinuousoperation can turn DSL data transmission on and off rapidly, and stay onor off for a time period as brief as the 250 microsecond duration ofeach Discrete Multi-Tone (DMT) DSL data symbol. According to oneembodiment, discontinuous operation still provides for transmission ofsignal on the DSL line at a low level when considered “off” to carrypre-coding signals for vectoring. According to another embodiment, sometraffic may be queued and later sent as a group of traffic, together inone contiguous “on” burst. Further, many DSL transceiver functionalitiescan be turned off when discontinuous operation is not sending any data,resulting in a higher power reduction, in some instances, greater than50%.

In OFF times data is generally not transmitted, however for vectoredsystems the signals from the vector pre-coder may continue to betransmitted downstream. A variant of discontinuous operation onlysuspends data transmission on some frequencies but continues to transmitdata on other frequencies during OFF times, this may be done toeliminate time-varying crosstalk into other services such as ADSL thatoperate only on some overlapping frequencies. Another variant ofdiscontinuous operation completely suspends data transmission on somefrequencies and occasionally sends signals only on other frequenciesduring ON times for uses such as “keep-alive” signaling forsynchronization, channel/crosstalk tracking, and operations/maintenancesignaling, which may be done to save additional power

Discontinuous operation should be controlled, and may need tooccasionally transmit signals at various frequencies for channel orcrosstalk estimation, such as occasionally transmitting on allfrequencies, or transmitting on different frequencies at different timesso that eventually all or most frequencies are used and are thereforetracked. Discontinuous operation may be pre-defined to only transmitsome discrete multi-tone (DMT) symbols (e.g., transmit even numberedsymbols or just synch symbols), or the symbols to transmit may beselected on-the-fly depending on current traffic. Entire super-framesmay be transmitted or not. Discontinuous operation should support some(programmable) minimum bit rate.

In an alternative embodiment, multiple sub-states are defined fordiscontinuous operation with different transmit power and transmit PSDlevels, so that there are multiple sub-states of L2.2. According toanother embodiment, Save Our Showtime (SOS) is incorporated as a powerstate, or SOS is used for power state transitions. SOS is described inITU-T G.993.2, and is designed to allow a pair of DSL modems to rapidlyadapt to changes in the noise environment on the DSL line to which theyare coupled with a rapid change in aggregate bit-rate. Further,low-power state transitions can be controlled via an on-linereconfiguration (OLR) procedure.

An aspect of one embodiment of the invention is to control the operationof low-power modes so that they do not decrease the stability of nearbyDSL lines that receive crosstalk. Three elements, according to variousembodiments, further this purpose: gradual exit from low-power states,discontinuous operation only at low transmit power, and an exchange ofdata and control information with a management system.

FIG. 4 illustrates an example state diagram 400 for different powerstates or modes (depicted by circles 405, 410, 415, 420 and 425), andallowed transitions between power states (lines with arrowheads showingthe direction of the allowed state transitions between different powerstates), according to embodiments of the invention. L0 at 405 is thefull power state and all other states are the above-described low-, orreduced-power states. FIG. 4 shows one example of a set of allowablestate transitions, but it is contemplated that the set of allowablestate transitions can be programmable, so that any state transition maybe enabled or disabled. For example, it may be desired in some cases toenable direct transitions from any one of the reduced-power states tothe L0 state, for example, if there is suddenly high user trafficdemand.

In the embodiment illustrated in FIG. 4, state diagram 400 includes fourlow-, or reduced-power modes, L2.0-X, L2.0-Y, L2.1 and L2.2. In L2.0-Xstate 410, transmit power spectral density (PSD) is lowered by “X” dBpower trim, and a low bit rate is maintained. In L2.0-Y state 415,transmit PSD is lowered by “Y” dB power trim, where “X”<“Y”, and a lowerbit rate is maintained. In L2.1 state 420, transmit PSD is lowered bythe maximum amount, and a very low bit rate is maintained. Finally, inIn L2.2 state 425, transmit PSD is lowered by the maximum amount, anextremely low bit rate is maintained, and, importantly, discontinuousoperation is enabled, in which the transmitting DSL signal is turned offfor brief periods of time.

L2, more generally, is considered a power management mode, which reducesthe power consumed by DSL modems (transceivers) for periods of time whenthere is little or no traffic on the line, such as according to ITU-TRecommendation G.992.3 (ADSL2) and Recommendation G.992.5 (ADSL2plus).During a reduced power mode, in one embodiment, the transmitted signalcan be modified by reducing the amplitude of the DSL signal during thetimes when data traffic sent by applications over the DSL connection isadequately small, thereby reducing the power consumed by the DSLtransceiver. For instance, the amplitude of each of the DMT tones (tonesare also called sub-carriers) can be reduced, including the number ofdata bits transmitted per tone. In one embodiment, the lower power modesreduce the power transmitted into the DSL line, thus reducing overallpower used by the DSL transceiver.

In one embodiment, application or user data sent over a DSL network maynot be transmitted over the DSL connection while a transmitting and areceiving pair of DSL transceivers is in an L2 mode; instead theinformation encoded over the DSL connection may be solely that requiredto keep the connection between the two DSL modems established andsynchronized, while allowing the DSL modems to exchange the messagesrequired to leave the L2 mode and return to normal transmission (modeL0) when application or user data is again available or ready fortransmission. In another embodiment, low-bitrate application data can betransmitted during an L2 mode, such as VoIP application data.

FIG. 5 depicts an illustrative embodiment 500 of power reductionsachieved during the showtime state, when a DSL modem enters areduced-power state such as L2.0, L2.1 and L2.2. These DSL low powermodes can enable a transmitting and receiving pair of DSL modemssupporting the DSL connection to enter and leave the lower power modeswhen low levels of data traffic, or no data traffic, are beingtransmitted over the DSL connection. The signal transmitted during themodes can keep the connection between the two DSL modems established andsynchronized, and the signal can return to full-power data transmissioncapabilities as soon as a high-bit-rate application makes such arequest. Entering into a reduced power mode and leaving the reducedpower mode can occur fast enough so that the application processes ateach end of the DSL connection dealing with the transferred data are notaffected by the transitions from an L2.x mode back to the L0 normaltransmission mode.

As a result of the intermittent nature of data packets to and from a DSLcustomer, the DSL line may frequently transition between the full power(L0) and various of the low power (L2.x) modes. These transitionsbetween the L0 and the L2.x modes may occur as frequently as once everyone or two seconds due to relatively short but frequent gaps in the DSLuser's data stream. Additionally these transitions into and out of theL2.x modes can occur at varying and unpredictable intervals based solelyon the specific nature of the communications carried over the DSLconnection. The occurrence of such transitions can be difficult tocharacterize or predict. Both of these characteristics of thetransitions can cause frequent fluctuations in the transmitted spectrumand signal level from a DSL modem transitioning between the L0 an L2.xmode. These changes can occur at various and unpredictable times.

As discussed elsewhere in this document, crosstalk is the resultingsignal coupled to other lines in the cable, which will correspondinglyfluctuate with the transitions between the L0 mode and one of the L2.xmodes. Receivers on the other DSL lines in the same cable can see thiscrosstalk as noise. Fluctuating crosstalk, which is known asnon-stationary or time-varying crosstalk, can be more disruptive to thedecoding of the signal by the receiving DSL modem than constantcrosstalk because it is difficult for a receiver to adapt to thechanging noise level.

In FIG. 5, the low-power state transitions, according to embodiments ofthe invention, are limited by the control of low-power mode (LPM)management information database (MIB) elements to limit time-varyingcrosstalk for stability. In particular, the maximum aggregate transmitpower increase (L2-ATPRINC) LPM MIB element limits the levels of eachpower increase and the minimum L2 time interval between L2 powerincreases (L2-TIMEINC) LPM MIB element limits the minimum time betweeneach power increase. The use of discontinuous operation in state L2.2 at425 is shown to be at a transmit PSD level below the highest level thatallows nearby DSL lines to be stable, and is referred to herein as themaximum stable discontinuous transmit power level. The maximum stablediscontinuous transmit power level equals full power lowered by theminimum stable discontinuous transmit power trim (L2.2-MIN).

FIG. 6 illustrates further DSL line and low-power state transitions,according to embodiments of the invention, limited by the control oflow-power mode (LPM) management information database (MIB) elements.According to the embodiments, LPM MIB elements such as: the aggregatetransmit power reduction (L2-ATPR) 605 limits the level of each powertrim; the total maximum aggregate transmit power reduction in L2(L2-ATPRT) 610 limits the total level of power trimming; the minimum L0time interval between L2 exit and the next L2 entry (L0-TIME) 615 limitsthe minimum time in L0 before a power trim; the minimum L2 time intervalbetween L2 entry and the first L2 trim (L2-TIME) 620 limits the minimumtime between power trims; and the minimum time interval between L2.1 andL2.2 (L2.1-TIME) 625 limits the minimum time between entering L2.1 ordropping below the maximum stable discontinuous transmit power level andthen transitioning to discontinuous operation in L2.2.

Gradual Exit

Prior art DSL low-power modes do not allow a gradual exit to full-power,the logic being that when a user wants to transmit or receive data overa DSL line, the user wants to do so with no delay. There are twopotential problems with this: quick exit to full power createspotentially damaging large increases in crosstalk in nearby DSL lines,and the alleged need to quickly exit to full power is based on a naïveview of user-perceived Quality of Experience (QoE).

A DSL line can be in low power state for a time period during whichother nearby DSL lines adapt to the low crosstalk caused by thelow-power DSL line. Then, the low-power DSL line abruptly transitions tofull power, and the neighboring DSL lines receiving crosstalk from itexperience a correspondingly large increase in crosstalk. If thecrosstalk and noise increases by more than their signal-to-noise ratio(SNR) margin, then the nearby DSL lines experiencing this crosstalk andnoise will become unstable and re-start or resynchronize.Resynchronization may also be induced by errors caused by the suddencrosstalk increase. If a low-power DSL line increases it's transmitpower by x dB, then the SNR margin of nearby DSL lines receivingcrosstalk from that DSL line can decrease by up to x dB, in the worstcase. Typical DSL line SNR margin is 6 dB, and 9-30 dB power reductionmay be enabled in low-power states, so rapid exit from low-power statescan often be sufficient to cause nearby DSL lines to become unstable.

Embodiments of the invention enable a controlled gradual increase intransmit power, or transmit power and bit rate, on a DSL line, for agradual exit from low-power states. If a first DSL line exits alow-power state then it may only increase transmit power by a limitedamount, for example, Y dB. If Y is less than the SNR margin of a second,nearby, DSL line, then the second DSL line can absorb a resultingincrease of up to Y dB in crosstalk power, for example, by usingseamless rate adaptation (SRA). SRA can lower the bit loading and ifneeded also lower the bit-rate in response to a crosstalk or a noiseincrease, and thereby restore the SNR margin. The speed of SRA isconfigurable, and it can be very rapid, in a few seconds. So, forexample, DSL line 1 in a low-power state can be configured, according toone embodiment, to increase transmit power by at most 3 dB, no moreoften than once every 2 seconds. In so doing, DSL line 2 receivingcrosstalk from DSL line 1 can adapt with SRA without having errors orresynchronization events. SRA lowers the rate of DSL line 2 receivingcrosstalk; however at most it is lowered to the rate attained withfull-power crosstalk from DSL line 1, which is the rate of crosstalkthat DSL line 2 would have had if DSL line 1 did not use low powerstates anyway.

QoE can be maintained with gradual exit from low-power states, either bymaking use of low-power states sufficiently infrequently (for exampleduring periods of reduced or no use of the DSL line), by interactingwith higher protocol layers, or by coordinating low-power state usagewith a management system. It's not uncommon for a user to wait 10seconds to even a minute or more to start-up a personal computer, or tobegin watching a video, or to receive a large download of information,etc. Thus, the user will tolerate some amount of time for an exit fromlow-power state. The exit may occur after receiving a notification (forexample, passed through the transceiver to the physical layer) of animpending traffic increase sent from an application or higher layer.Low-power states can be coordinated with resource allocation and sessioninitiation. A notification of a session initiation may simply indicatethat a high-traffic session is impending, or it may also indicate theimpending level of traffic and when it will start. An indication ofsupport for such session notification should be reported. For example, aDSLAM may send a query to a user CPE device to determine whether thedevice is capable of supporting session notification. If the CPEresponds affirmatively, the DSLAM may then transmit the notification.Other notifications between layers can assist QoE with low-power states.

Gradual wake up performed purely at the physical layer can disruptcertain types of internet traffic, such as VoIP traffic, since a burstof new traffic can cause the internet traffic to be delayed or droppedbefore power and bit-rate are increased if there is only a singlephysical layer queue. Interaction with higher layers can limittime-varying crosstalk without impacting QoE. According to oneembodiment, one solution is to maintain a high-priority queue forcertain types of susceptible traffic, such as VoIP traffic.

Management System

In one embodiment, low-power states can be configured with settings(such as threshold information that indicates a certain amount of datamay be transmitted for a certain period of time) that should suffice inmost cases and then the DSL lines may run autonomously. However,performance may be significantly increased if a DSL management systemcollects data and adjusts settings to improve performance with low-powerstates. Performance includes factors such as bit rates, error rates,line stability, and power consumption. Data can be collected on theactual use of the low power states, the DSL line transmissionenvironment, DSL line status, test, diagnostics, and performancemonitoring data. The management system can be a Spectrum ManagementCenter (SMC) for Dynamic Spectrum Management (DSM), or for Dynamic LineManagement (DLM). The management system can communicate over a networkto the DSL equipment and be located in remote servers or in the cloud,and so it can support long-term data storage and high-power computing.

A management system can maintain a long-term traffic history of lineusage, traffic patterns, etc., and use this historic information tocreate a policy for DSL line low-power state transitions. For example,in one embodiment, it may be determined that a DSL line is rarely activebetween certain hours of the day, or with days of the week, and then lowpower states are enabled only during these hours when traffic isquiescent. Or, it may be determined that if a DSL line is quiescent forsome number hours, then it is likely to remain quiescent for someadditional number of hours, then low power states are enabled onlyduring those additional hours.

The combined use of different transmission power states can beintelligently managed by a local real-time controller, a remotemanagement system, or a combination of both. The real-time controllermay reside in or near the user CPE or DSLAM, or both. Sufficient dataand management controls are defined so that the management system candetermine which settings to apply to different DSL transceivers.

In one embodiment, the real-time controller determines when parameterlevels or combinations of parameter levels have reached values such ascrossing thresholds, for a sufficient of time, to initiate a transitionbetween different power states. The parameter levels can be trafficlevels, throughputs, queue lengths, bandwidth demand, number ofsessions, traffic descriptors, traffic predictions, time of day or timeof week, user data, or other external inputs. The real-time controllerimplements state transitions that are allowed, increases and decreasespower and PSD levels according to allowed levels, and affects statetransitions after certain lengths of waiting time or hysteresis. Thethresholds, allowed state transitions, allowed transmit power or PSDchanges, times, etc., can be maintained in a data store, such as amanagement information base (MIB) and are referred to herein as the “LPMMIB elements,” where LPM refers to Low-Power Mode.

According to one embodiment, the LPM MIB elements can be statically set,or occasionally updated by an external management system. LPM MIBelements should be set to accomplish one or more of the following:eliminate or minimize instability caused to other DSL lines, minimizedelay, maximize user-perceived QoE, and minimize power usage. The LPMMIB elements may be determined in an iterative “re-profiling” process,which sets MIB elements in the DSL transceivers, monitors performance ofthe DSL transceivers thusly configured, and then re-sets the MIBelements in an iterative loop until an acceptable level of performanceis achieved. MIB elements may also be computed, or extrapolated fromknown data, in one embodiment.

The management system may set MIB elements separately and independentlyon each DSL line, or the MIB elements may be jointly set across multipleDSL lines. DSL lines in the same cable, binder, neighborhood, orgeographic area may be grouped for jointly determining MIB elements. Forexample, in one embodiment, various LPM MIB elements may be changed onDSL line 1, then DSL line 2 monitored to see if it is stable in view ofany crosstalk induced from DSL line 1 with these settings. Thismonitoring data is then used to determine jointly acceptable LPM MIBelement settings.

In many cases, it may be that the time-varying crosstalk from a DSL linechanging power states will have little or no impact on other, nearby,DSL lines. In these cases the management system can safely set LPM MIBelements more aggressively for high power savings and low delay,allowing for rapid wake up or the use of discontinuous operation atrelatively high power levels.

In one embodiment of the invention, low-power state transitions arecontrolled so that they do not cause instability on nearby DSL linesreceiving crosstalk. Control is primarily done by limiting each increasein transmit PSD and transmit power, how often these increases may occur,and the maximum transmit power and transmit PSD with discontinuousoperation. These limits are generally controlled via LPM MIB elements,and they can vary line-by-line and can be determined in different ways,such as: overall via offline studies, dynamically via managementre-profiling, dynamically via calculation, and estimated or extrapolatedfrom known data, or from data from nearby DSL lines.

Channel Tracking

Current standards such as ADSL2/ADSL2plus [ITU-T G.992.3/G.992.5] do notallow bitswap (i.e., switching subcarriers) in low-power states. Also,when exiting to full-power state the bits (bi) table and gains (gi)table that were last used in full-power state are generally usedregardless of any changes in the channel environment that occurredduring low-power states, such as the DSL environment noise, crosstalk innearby DSL lines, or channel response. Embodiments of this invention canenable bitswap, SRA, other online reconfiguration (OLR) functions, andchannel tracking while in low-power states. The bit loading (bi) andgains (gi) tables may be set based on the DSL environment immediatelybefore making a power state transition, as well as accounting for thepreviously known environment values.

Transition to higher speed transmit power states may be rapid orgradual. The bi values applied in the L0 state or another higher speedstate can extrapolated from the bi values in the current VDSL2 LPM, andthese bi can also be extrapolated from, or simply use, stored valuesthat were used in previous occupancy of that LPM state. Note that thisextrapolation should be conservative, with low bi values applied whenfirst entering the L0 state to avoid a re-train of the DSL line. The bivalues in the L0 state may be subsequently improved with SRA.

It may be difficult to maintain synchronization and accurate channel andnoise estimation for a DSL line during discontinuous operation of theDSL line, particularly if the DSL line is quiescent for long timeperiods. Embodiments of the invention can control the minimum durationof “on” times and the maximum duration of “off” times in discontinuousoperation to ensure continued synchronization and channel tracking.Embodiments can periodically transmit symbols to maintainsynchronization, including synchronization symbols. Thesesynchronization symbols can be dummy symbols if there is insufficientdata traffic. With vectoring, channel tracking includes tracking thecrosstalk channels. The rate of recurrence of transmitting channelestimation sequences for vectoring can be enabled and controlled toensure accurate vectoring crosstalk channel estimation withdiscontinuous operation.

PSD Shaping

FIG. 7 illustrates at 700 examples of different transmitted low-powermode (LPM) power spectral densities (PSDs) according to embodiments ofthe invention. These examples are downstream VDSL transmit PSDs, but theshaping could be performed upstream or with other systems such asG.fast. For comparison, a full power (L0) transmit PSD is shown at 705.A flat power back-off (PBO) LPM PSD is shown at 710, a simple LPM PSDthat only transmits on low frequencies is shown at 715, and a shaped LPMPSD is shown at 720. Transitioning into a low power state often altersthe transmit power spectral density (PSD), changing it to an “LPM PSD.”This LPM PSD can have a simple flat power backoff (PBO) illustrated at715, which lowers the transmit PSD by the same amount at everyfrequency, in one embodiment. Some sub-carriers may be turned off andnot used. In another embodiment, frequency-shaped LPM PSDs 720 are usedin low-power states. Low frequencies experience lower attenuation thanhigh frequencies, and so low-power states may concentrate transmit powerat low frequencies. The transmitted LPM PSD can be shaped and optimizedby the management system for power savings. This shaping can simplyreduce the number of active frequency tones such as using only lowfrequencies, or it can result from a more complex optimization withrespect to a three-way tradeoff in power usage, line performance, andcrosstalk impact.

LPM and Vectoring

The use of low power states described herein can be combined withvectoring. The vector pre-coder in the DSLAM or VTU-O is ideallyconfigured with coefficients that result in cancellation of all the farend cross talk (FEXT) in the vectored group received at the CPE orVTU-R. However, as the transmit power is varied or when DSL lines aretemporarily shut down due to going into low power states, then thevector precoder coefficients can differ from their ideal values,resulting in loss of SNR margin. There are two ways of mitigating thisloss: update the vector precoder coefficients as lines in the vectoredgroup change power state, or ensure there is sufficient SNR margin tocontinue operation of the line as the vector precoder coefficientsdiffer from their ideal values. Vectoring precoder coefficients can becoordinated and updated as DSL lines with crosstalk canceled byvectoring go in and out of low-power states or vary transmit power.Discontinuous operation can be coordinated with vector precoding tocontrol and handle the SNR degradation caused by DSL lines turning offand on. The rate of recurrence and size of power increase steps may bechanged if all the time-varying crosstalk is within a single vectoredgroup of DSL lines or otherwise mutually crosstalk cancelled, from thesettings that would be used between DSL lines that are not mutuallycrosstalk cancelled.

G.fast

The emerging ITU G.fast specification uses time-division duplex (TDD),which alternately transmits downstream and upstream. TDD can beconsidered a type of discontinuous operation and it generatestime-varying crosstalk that may harm other systems sharing the samecable. In particular, VDSL lines can share the same frequencies asG.fast, with the lower G.fast frequencies overlapping VDSL frequencies.VDSL refers to any VDSL variant including VDSL1, VDSL2, and vectoredVDSL2. The transmit PSD of the G.fast system may be lowered within theVDSL bands, to levels such that the G.fast crosstalk does notdestabilize VDSL lines. In one embodiment, this may be doneasymmetrically, with different PSD levels upstream and downstream, andit can have different PSD levels in the upstream and downstream VDSLbands. The G.fast transmit PSD level within the VDSL bands can be set toenable compatibility with VDSL, to lower G.fast power usage, or both.

Example Definitions of LPM MIB Elements

These LPM MIB elements are used for configuration and control of VDSL2LPM. They can also be used to query or monitor LPM status.

Power Management State Forced (PMSF). This configuration parameterdefines the DSL line states to be forced by the near-end xTU on this DSLline. It is coded as an integer value.

Power Management State Enabling (PM Mode). This configuration parameterdefines the DSL line states the xTU-C or xTU-R may autonomouslytransition to on this DSL line.

Minimum L0 time interval between L2 exit and next L2 entry (L0-TIME).This parameter represents the minimum time (in seconds) between an exitfrom the L2 state and the next entry into the L2 state.

Minimum L2 time interval between L2 entry and first L2 trim (L2-TIME).This parameter represents the minimum time (in seconds) between an entryinto the L2 state and the first power trim in the L2 state and betweentwo consecutive power trims in the L2 state.

Maximum aggregate transmit power reduction per L2 request or L2 powertrim (L2-ATPR). This parameter represents the maximum aggregate transmitpower reduction (in dB) that can be performed in the L2 request (i.e. attransition from L0 to L2 state) or through a single power trim in the L2state.

Total maximum aggregate transmit power reduction in L2 (L2-ATPRT). Thisparameter represents the total maximum aggregate transmit powerreduction (in dB) that can be performed in an L2 state.

Minimum L2 time interval between L2 power increases (L2-TIMEINC). Thisparameter represents the minimum time (in seconds) between entry into L2low power state and the first L2 power increase request and between twoconsecutive L2 power increase requests.

Minimum L2 time interval in L2.2 (L2.2-TIMEINC). This parameterrepresents the minimum time (in seconds) between entry into L2.2 lowpower state and the first power increase request.

Maximum aggregate transmit power increase per L2 power increase(L2-ATPRINC). This parameter represents the maximum transmit powerincrease (in dBm) that is allowed in an L2 power increase request.

Minimum time interval between L2.1 and L2.2 (L2.1-TIME). This parameterlimits the minimum time (in seconds) between entering L2.1 and thentransitioning to discontinuous operation in L2.2.

Minimum stable discontinuous transmit power trim (L2.2-MIN). Thisparameter represents the minimum decrease in aggregate transmit powerlevel which may be used in low-power state L2.2, This level is the dBmdecrease below the maximum aggregate downstream transmit power [G.993.2Table 6 1].

Allowed State Transitions (LPM STATE TRANS). For every pair of distinctpower states (A, B), a transition from A to B is either enabled ordisabled, where A, B are elements of {L0, L2.0, L2.1, L2.2}. Encoded asa 12-bit bitmap.

Minimum data rate in L2.2 (L2-2 MIN DATA): This parameter is the minimumdata rate that is supported during operation in L2.2 low-power mode.

Minimum discontinuous on time (MIN-ON). This parameter is the minimumtime (in seconds) of a distinct on time period or contiguous burst oftransmission during discontinuous operation in L2.2 state.

Maximum discontinuous off time (MAX-OFF). This parameter is the maximumtime (in seconds) of a distinct off time period or a contiguousquiescent transmitter time period during discontinuous operation in L2.2state.

LPM state-transition increase traffic threshold (LPM-THRESHINC). Thisparameter is defined as the data rate threshold between each adjacentstate and sub-state that traffic rates must be exceeded to start and runa time counter for a state transition to increase power. Defined as a12-octet bit map, with each octet indicating the percentage of ATTNDR(0-100%) on this DSL line. Exceeding this traffic threshold starts acounter that runs as long as the threshold condition holds, and causes apower state transition if the counter exceeds the appropriate timeinterval; L2-TIMEINC or L2.2-TIMEINC.

LPM state-transition decrease traffic threshold (LPM-THRESHDEC). Thisparameter is defined as the data rate threshold between each adjacentstate and sub-state that traffic rates must be below to start and run atime counter for a state transition to decrease power. Defined as a12-octet bit map, with each octet indicating the percentage of ATTNDR(0-100%) on this line. Being below this threshold starts a counter thatruns as long as the threshold condition holds, and causes a power statetransition if the counter exceeds the appropriate time interval;L2-TIMEINC or L2.2-TIMEINC.

LPM data rate (LPM-DATARATE) (read only). This parameter is defined asthe data rate during the most recent occupancy of each LPM state andsub-state. Defined as two octets representing data rate in units of 20kbps from 0 to 1.31068 Gbps, with special value FFFF indicating morethan 1.31068 Gbps.

Indication of support for traffic prioritization (HIQUEUE). Thisparameter indicates that the transceiver supports prioritization ofhigh-priority traffic such as VoIP within the transceiver queues.Boolean, read-only.

LPM queue depth (HIQUEUE DEPTH). Indicates the depth of the queue(kBytes) that supports high-priority traffic. Supported ifHIQUEUE==true. Read-only.

Indication of support for notification of an impending session(SESSION). This parameter indicates that the transceiver supports thatthe notification of an impending high-traffic session initiates an exitfrom low-power states to full-power. Boolean, read-only.

Indication of impending session start (SESSION IMPENDING). Thisparameter notifies the transceiver that a new high-traffic session isimpending. Upon reception, the transceiver begins exiting low-powerstates to full-power.

Additionally, performance can be monitored with existing parameters suchas: actual data rate, actual noise margin, ACTATP; as well as with theerror counters such as: CV-C, FECS-L, ES-L, SES-L, LOSS-L, and UAS-L.Thus, embodiments described herein provide for a method and apparatusfor operating a transceiver coupled to a digital subscriber line (DSL)line, comprising reducing a transmit power level of the transceiver froma first transmit power level sufficient for the transceiver tocontinuously transmit data on the DSL line at a first bit rate to asecond transmit power level below the first transmit power levelsufficient for the transceiver to continuously transmit data on the DSLline at a second bit rate that is lower than the first bit rate andwithout generating time-varying crosstalk sufficient to destabilize anearby DSL line, and repeatedly suspending the transceiver fromtransmitting data on the DSL line for a period of time withoutgenerating further time-varying crosstalk sufficient to destabilize thenearby DSL line and only while the transmit power level of thetransceiver is reduced to the second transmit power level.

In one embodiment, the second bit rate that is lower than the first bitrate on the DSL line is sufficient for the transceiver to transmit Voiceover Internet Protocol (VoIP) data, keep alive data, or both; on the DSLline.

Further, repeatedly suspending the transceiver from transmitting data onthe DSL line for a period of time comprises one of: turning offtransmitter functionality of the transceiver; turning off receiverfunctionality of the transceiver; turning off the transmitterfunctionality of the transceiver for a period of time no longer thanrequired to maintain synchronization of, or to track channel variationsin, the DSL line; turning off the transmitter functionality of thetransceiver for a period of time at least equal to a duration of timeneeded to transmit a discrete multi-tone (DMT) symbol; transmittingpre-coding signals for use in vectoring; and turning off a plurality oftransceiver functionalities to decrease transceiver power consumption.

In one embodiment, the second transmit power sufficient for thetransceiver to continuously transmit data on the DSL line at a secondbit rate is selected from one of a group of low-power mode (LPM) PSDsconsisting of: a downstream transmit PSD, an upstream transmit PSD, aflat power back-off (PBO) PSD, a simple LPM PSD that only transmits onlow frequencies, and a frequency-shaped LPM PSD.

In one embodiment, repeatedly suspending the transceiver fromtransmitting data on the DSL line for a period of time involvesrepeatedly suspending the transceiver from transmitting data on a subsetof sub-carrier frequencies on the DSL line while at the same time thetransceiver continues to transmit data on the other sub-carrierfrequencies not in the subset on the DSL line.

In one embodiment, increasing the transmit power level of thetransceiver from the second transmit power level sufficient for thetransceiver to continuously transmit data on the DSL line at the secondbit rate to the first transmit power level sufficient for thetransceiver to continuously transmit data on the DSL line at the firstbit rate is accomplished without generating crosstalk sufficient todestabilize the nearby DSL line. In one embodiment, this is accomplishedby controlling the increase in the transmit power level according to aplurality of values of transceiver configuration and operationparameters maintained in a data store to limit time-varying crosstalk inthe nearby DSL line. Further, increasing the transmit power level of thetransceiver from the second transmit power level to the first transmitpower level comprises, in one embodiment, increasing the transmit powerlevel from the first transmit power level to the second transmit powerlevel in a series of steps incurred over a duration of time, in whichfor each step a maximum increase in the transmit power level is allowedsuch that transmitting data on the DSL line does not generate crosstalksufficient to destabilize the nearby DSL line. Each step is of a minimumduration of time sufficient to allow the nearby DSL line to adapt to anychange in crosstalk, generated by data being transmitted on the DSLline, without incurring errors, a restart, or a resynchronization of thenearby DSL line. The nearby DSL line adapts to any change in crosstalkgenerated by data being transmitted on the DSL line using seamless rateadaptation (SRA).

In one embodiment, the transceiver configuration and operationparameters maintained in a data store comprise a number of managementinformation base (MIB) elements relating to configuration and operationof the transceiver and maintained in a MIB database. The MIB elementsmay each be set to a value according to an iterative process comprisingthe steps of: setting the values of one or more of the plurality of MIBelements in the transceiver; monitoring performance of the transceiverwith the values as set; and resetting the values of one or more of theplurality of MIB elements in the transceiver responsive to monitoringthe performance.

In one embodiment, the iterative process further comprises: monitoringthe nearby DSL line for stability while performing the iterativeprocess; and setting the values of one or more of the MIB elements inthe transceiver further responsive to the monitoring of the nearby DSLline.

In one embodiment, the MIB elements are associated with each of aplurality of transceivers each coupled to a corresponding plurality ofDSL lines, wherein a DSL line is selected to be in the correspondingplurality of DSL lines based on one or more of: crosstalk levels betweenthe DSL line and a nearby DSL line; the loop, cable, and/or binder inwhich the DSL line exists; neighborhood information; and geographicdata.

Further embodiments contemplate storing prioritized traffic in atransmit data queue associated with the transceiver when the transceiveris suspended from transmitting data on the DSL line for a period oftime, and from which to transmit the prioritized traffic when thetransceiver is no longer suspended from transmitting data on the DSLline. Alternatively, embodiments contemplate storing prioritized trafficin a transmit data queue associated with the transceiver when thetransceiver is operated at a second bit rate that is lower than thefirst bit rate for a period of time, while not transmitting traffic thatis not stored in the prioritized traffic transmit data queue.

In embodiments of the invention, repeatedly suspending the transceiverfrom transmitting data on the DSL line for a period of time furtherinvolves controlling a minimum duration of time during with thetransceiver is transmitting data, including a synchronization symbol, onthe DSL line between the periods of time during which the transceiver issuspended from transmitting data on the DSL line to ensuresynchronization and channel tracking of the DSL line. Repeatedlysuspending the transceiver from transmitting data on the DSL line for aperiod of time may also involve controlling a maximum duration of timeduring which the transceiver is suspended from transmitting data on theDSL line to ensure synchronization and channel tracking of the DSL line.

In some embodiments, reducing a transmit power level of the transceiverfrom a first transmit power level sufficient for the transceiver tocontinuously transmit data on the DSL line at a first bit rate to asecond transmit power level below the first transmit power levelsufficient for the transceiver to continuously transmit data on the DSLline at a second bit rate that is lower than the first bit ratecomprises shaping a transmit power spectral density (PSD) to vary theextent to which to reduce the transmit power level for differenttransmit frequency bands.

Other embodiments include updating a signal to noise ratio (SNR) marginto account for mis-matched vector precoder coefficient values associatedwith the DSL line, responsive to repeatedly suspending the transceiverfrom transmitting data on the DSL line for a period of time. Additionalembodiments comprise updating vector precoder coefficient valuesassociated with the DSL line, responsive to repeatedly suspending thetransceiver from transmitting data on the DSL line for a period of time,to avoid signal to noise ratio (SNR) degradation of the nearby DSL linethat may be caused by the repeated suspensions.

If the transceiver is a G.fast transceiver, reducing the transmit powerlevel of the transceiver from the first transmit power level to thesecond transmit power level comprises reducing the transmit power levelof the G.fast transceiver within low frequency bands to enable operationof the DSL line in a cable or loop or binder comprising other DSL linesoperating according to a Very high speed/Very high bit rate DSL (VD SL)standard.

CONCLUSION

In this description, numerous details have been set forth to provide amore thorough explanation of embodiments of the present invention. Itshould be apparent, however, to one skilled in the art, that embodimentsof the present invention may be practiced without these specificdetails. In other instances, well-known structures and devices have beenshown in block diagram form, rather than in detail, in order to avoidobscuring embodiments of the present invention.

Some portions of this detailed description are presented in terms ofalgorithms and symbolic representations of operations on data within acomputer memory. These algorithmic descriptions and representations arethe means used by those skilled in the data processing arts to mosteffectively convey the substance of their work to others skilled in theart. An algorithm is here, and generally, conceived to be aself-consistent sequence of steps leading to a desired result. The stepsare those requiring physical manipulations of physical quantities.Usually, though not necessarily, these quantities take the form ofelectrical or magnetic signals capable of being stored, transferred,combined, compared, and otherwise manipulated. It has proven convenientat times, principally for reasons of common usage, to refer to thesesignals as bits, values, elements, symbols, characters, terms, numbers,or the like.

It should be borne in mind, however, that all of these and similar termsare to be associated with the appropriate physical quantities and aremerely convenient labels applied to these quantities. Unlessspecifically stated otherwise, as apparent from this discussion, it isappreciated that throughout the description, discussions utilizing termssuch as “processing” or “computing” or “calculating” or “determining” or“displaying” or the like, refer to the action and processes of acomputer system, or similar electronic computing device, thatmanipulates and transforms data represented as physical (electronic)quantities within the computer system's registers and memories intoother data similarly represented as physical quantities within thecomputer system memories or registers or other such information storage,transmission or display devices.

Embodiments of present invention also relate to apparatuses forperforming the operations herein. Some apparatuses may be speciallyconstructed for the required purposes, or it may comprise a generalpurpose computer selectively activated or reconfigured by a computerprogram stored in the computer. Such a computer program may be stored ina computer readable storage medium, such as, but not limited to, anytype of disk including floppy disks, optical disks, CD-ROMs, DVD-ROMs,and magnetic-optical disks, read-only memories (ROMs), random accessmemories (RAMs), EPROMs, EEPROMs, NVRAMs, magnetic or optical cards, orany type of media suitable for storing electronic instructions, and eachcoupled to a computer system bus.

The algorithms and displays presented herein are not inherently relatedto any particular computer or other apparatus. Various general-purposesystems may be used with programs in accordance with the teachingsherein, or it may prove convenient to construct more specializedapparatus to perform the required method steps. The required structurefor a variety of these systems appears from the description herein. Inaddition, embodiments of the present invention are not described withreference to any particular programming language. It will be appreciatedthat a variety of programming languages may be used to implement theteachings of the invention as described herein.

A machine-readable medium includes any mechanism for storing ortransmitting information in a form readable by a machine (e.g., acomputer). For example, a machine-readable medium includes read onlymemory (“ROM”); random access memory (“RAM”); magnetic disk storagemedia; optical storage media; flash memory devices; etc.

What is claimed is:
 1. A method for operating a transceiver coupled to adigital subscriber line (DSL) line, comprising: reducing a transmitpower level of the transceiver from a first transmit power levelsufficient for the transceiver to continuously transmit data on the DSLline at a first bit rate to a second transmit power level below thefirst transmit power level sufficient for the transceiver tocontinuously transmit data on the DSL line at a second bit rate that islower than the first bit rate and without generating time-varyingcrosstalk sufficient to destabilize a neighboring DSL line; andrepeatedly suspending the transceiver from transmitting data on the DSLline for a period of time without generating further time-varyingcrosstalk sufficient to destabilize the neighboring DSL line and whilethe transmit power level of the transceiver is reduced to the secondtransmit power level.
 2. The method of claim 1, wherein the second bitrate that is lower than the first bit rate on the DSL line is sufficientfor the transceiver to transmit one or more of Voice over InternetProtocol (VoIP) data, or keep alive data; on the DSL line.
 3. The methodof claim 1, wherein repeatedly suspending the transceiver fromtransmitting data on the DSL line for a period of time comprises one of:turning off transmitter functionality of the transceiver; turning offreceiver functionality of the transceiver; turning off the transmitterfunctionality of the transceiver for a period of time no longer thanrequired to maintain synchronization of, or to track channel variationsin, the DSL line; turning off the transmitter functionality of thetransceiver for a period of time at least equal to a duration of timeneeded to transmit a discrete multi-tone (DMT) symbol; transmittingpre-coding signals for use in vectoring; or turning off a plurality oftransceiver functionalities to decrease transceiver power consumption.4. The method of claim 1, wherein the second transmit power sufficientfor the transceiver to continuously transmit data on the DSL line at asecond bit rate is selected from one of a group of low-power mode (LPM)PSDs which includes one of: a downstream transmit PSD, an upstreamtransmit PSD, a flat power back-off (PBO) PSD, a simple LPM PSD thatonly transmits on some frequencies, or a frequency-shaped LPM PSD. 5.The method of claim 1, wherein repeatedly suspending the transceiverfrom transmitting data on the DSL line for a period of time comprisesrepeatedly suspending the transceiver from transmitting data on a subsetof a plurality of sub-carrier frequencies on the DSL line while thetransceiver continues to transmit data on other of the plurality ofsub-carrier frequencies not in the subset on the DSL line.
 6. The methodof claim 1, further comprising increasing the transmit power level ofthe transceiver from the second transmit power level sufficient for thetransceiver to continuously transmit data on the DSL line at the secondbit rate to the first transmit power level sufficient for thetransceiver to continuously transmit data on the DSL line at the firstbit rate and without generating crosstalk sufficient to destabilize theneighboring DSL line.
 7. The method of claim 6, wherein increasing thetransmit power level of the transceiver from the second transmit powerlevel to the first transmit power level comprises controlling theincrease in the transmit power level according to a plurality of valuesof transceiver configuration and operation parameters maintained in adata store to limit time-varying crosstalk in the neighboring DSL line.8. The method of claim 6, wherein increasing the transmit power level ofthe transceiver from the second transmit power level to the firsttransmit power level comprises increasing the transmit power level fromthe first transmit power level to the second transmit power level in aseries of operations incurred over a duration of time, in which for atleast one operation a maximum increase in the transmit power level isallowed such that transmitting data on the DSL line does not generatecrosstalk sufficient to destabilize the neighboring DSL line.
 9. Themethod of claim 8, wherein the at least one operation is of a minimumduration of time sufficient to allow the neighboring DSL line to adaptto any change in crosstalk, generated by data being transmitted on theDSL line, without incurring errors, a restart, or a resynchronization ofthe neighboring DSL line.
 10. The method of claim 9, wherein theneighboring DSL line is to adapt to any change in crosstalk generated bydata being transmitted on the DSL line using seamless rate adaptation(SRA).
 11. The method of claim 7, wherein the transceiver configurationand operation parameters maintained in a data store comprise a pluralityof management information base (MIB) elements relating to configurationand operation of the transceiver and maintained in a MIB database. 12.The method of claim 11, wherein at least one of the plurality of MIBelements is set to a value according to an iterative process comprisingthe operations of: setting the values of one or more of the plurality ofMIB elements in the transceiver; monitoring performance of thetransceiver with the values as set; and resetting the values of the oneor more of the plurality of MIB elements in the transceiver responsiveto monitoring the performance.
 13. The method of claim 12, furthercomprising: monitoring the neighboring DSL line for stability whileperforming the iterative process; and setting the values of the one ormore of the MIB elements in the transceiver further responsive to themonitoring of the neighboring DSL line.
 14. The method of claim 11,wherein the plurality of MIB elements are associated with at least oneof a plurality of transceivers, at least one of which is coupled to acorresponding plurality of DSL lines, wherein a DSL line is selected tobe in the corresponding plurality of DSL lines based on one or more of:crosstalk levels between the DSL line and a nearby DSL line; the loop,cable, and/or binder in which the DSL line exists; neighborhoodinformation; or geographic data.
 15. The method of claim 1, furthercomprising storing prioritized traffic in a transmit data queueassociated with the transceiver when the transceiver is suspended fromtransmitting data on the DSL line for a period of time, and from whichto transmit the prioritized traffic when the transceiver is no longersuspended from transmitting data on the DSL line.
 16. The method ofclaim 1, further comprising storing prioritized traffic in a transmitdata queue associated with the transceiver when the transceiver isoperated at the second bit rate that is lower than the first bit ratefor a period of time, while not transmitting traffic that is not storedin the prioritized traffic transmit data queue.
 17. The method of claim1, wherein repeatedly suspending the transceiver from transmitting dataon the DSL line for a period of time further comprises controlling aminimum duration of time during with the transceiver is transmittingdata, including a synchronization symbol, on the DSL line between theperiods of time during which the transceiver is suspended fromtransmitting data on the DSL line to ensure synchronization and channeltracking of the DSL line.
 18. The method of claim 17, wherein repeatedlysuspending the transceiver from transmitting data on the DSL line forthe period of time further comprises controlling a maximum duration oftime during which the transceiver is suspended from transmitting data onthe DSL line to ensure synchronization and channel tracking of the DSLline.
 19. The method of claim 1, wherein reducing a transmit power levelof the transceiver from the first transmit power level sufficient forthe transceiver to continuously transmit data on the DSL line at a firstbit rate to a second transmit power level below the first transmit powerlevel sufficient for the transceiver to continuously transmit data onthe DSL line at the second bit rate that is lower than the first bitrate comprises shaping a transmit power spectral density (PSD) to varythe extent to which to reduce the transmit power level for differenttransmit frequency bands.
 20. The method of claim 6, further comprisingupdating a signal to noise ratio (SNR) margin to account for mismatchedvector precoder coefficient values associated with the DSL line,responsive to repeatedly suspending the transceiver from transmittingdata on the DSL line for a period of time.
 21. The method of claim 1,further comprising updating vector precoder coefficient valuesassociated with the DSL line, responsive to repeatedly suspending thetransceiver from transmitting data on the DSL line for a period of time,to avoid signal to noise ratio (SNR) degradation of the neighboring DSLline that may be caused by the repeated suspensions.
 22. The method ofclaim 1, wherein the transceiver is a G.fast transceiver and whereinreducing the transmit power level of the transceiver from the firsttransmit power level to the second transmit power level comprisesreducing the transmit power level of the G.fast transceiver within lowfrequency bands to enable operation of the DSL line in a cable or loopor binder comprising other DSL lines operating according to a Very highspeed or a Very high bit rate DSL (VDSL) standard.
 23. An apparatuscomprising: a controller to operate a transceiver coupled to a digitalsubscriber line (DSL) to: reduce a transmit power level of thetransceiver from a first transmit power level sufficient for thetransceiver to continuously transmit data on the DSL line at a first bitrate to a second transmit power level below the first transmit powerlevel sufficient for the transceiver to continuously transmit data onthe DSL line at a second bit rate that is lower than the first bit rateand without generating time-varying crosstalk sufficient to destabilizea neighboring DSL line; and repeatedly suspend the transceiver fromtransmitting data on the DSL line for a period of time withoutgenerating further time-varying crosstalk sufficient to destabilize theneighboring DSL line and while the transmit power level of thetransceiver is reduced to the second transmit power level.
 24. Theapparatus of claim 23, wherein the controller to repeatedly suspend thetransceiver from transmitting data on the DSL line for a period of timecomprises the controller to perform one or more of: turn off transmitterfunctionality of the transceiver; turn off receiver functionality of thetransceiver; turn off the transmitter functionality of the transceiverfor a period of time no longer than required to maintain synchronizationof, or to track channel variations in, the DSL line; turn off thetransmitter functionality of the transceiver for a period of time atleast equal to a duration of time needed to transmit a discretemulti-tone (DMT) symbol; transmit pre-coding signals for use invectoring; or turn off a plurality of transceiver functionalities todecrease transceiver power consumption.
 25. A computer-readablenon-transitory storage medium, comprising computer instructions, thatwhen executed, cause a transceiver coupled to a digital subscriber line(DSL) line, to perform a method, comprising: reducing a transmit powerlevel of the transceiver from a first transmit power level sufficientfor the transceiver to continuously transmit data on the DSL line at afirst bit rate to a second transmit power level below the first transmitpower level sufficient for the transceiver to continuously transmit dataon the DSL line at a second bit rate that is lower than the first bitrate and without generating time-varying crosstalk sufficient todestabilize a neighboring DSL line; and repeatedly suspending thetransceiver from transmitting data on the DSL line for a period of timewithout generating further time-varying crosstalk sufficient todestabilize the neighboring DSL line and while the transmit power levelof the transceiver is reduced to the second transmit power level.